There is evidence that a measure of the ultrasound nonlinear parameter (B/A) can be a good tissue classifier. Recently, the medical ultrasound community has witnesses a great deal of effort in this area. However, to date, all the reported techniques are either suitable only for transmission mode or require a multitude of ultrasound beams or frequencies (or both). These are, of course, server shortcomings as far as conventional pulse/echo B- mode ultrasound is concerned. We propose to undertake a program to develop a novel system which (1) operates in reflection, (2) uses only one ultrasound beam, and (3) operates with only one frequency. Our approach is based on variable amplitude excitation. We measure the echo amplitudes at a fixed point of the A-line for progressively increasing excitation amplitudes. Any deviation from linearity between the excitation amplitude and the echo amplitude then services as a measure of the integrated nonlinearity between the transducer and the defined point on the A-line. During Phase I, we propose to complete the instrumentation of a mechanically scanned system and demonstrate the feasibility of this concept. We would then like to develop special purpose imaging hardware, based on electronic scanning, in Phase 11.